At the present time, merchandising of an optical disc having a recording density of approximately 100 GB is possible for public welfare as well owing to Blu-ray Disc™ standard using a blue-violet semiconductor laser. Hereafter, implementation of a large capacity exceeding 500 GB is desired in the optical disc as well. For implementing such an ultrahigh density in the optical disc, however, a high-density technique according to a new system different from the conventional high-density technique using a shorter wavelength and a higher NA of the object lens is necessary.
In the midst of studies concerning a storage technique of next generation, the hologram recording technique of recording digital information by utilizing the holography attracts attention. As for the hologram recording technique, there is, for example, JP-A-2004-272268 (Patent Literature 1). JP-A-2004-272268 describes the so-called angular multiplexing recording system, in which different page data is displayed on a spatial light modulator while an incidence angle of a reference beam onto optical information recording media is changed and multiplexing recording is conducted. In addition, JP-A-2004-272268 describes a technique of shortening the spacing between adjacent holograms by focusing a signal beam with a lens and disposing an aperture (spatial filter) in its beam waist.
Furthermore, as for the hologram recording technique, there is, for example, WO2004-102542 (Patent Literature 2). In an example using a shift multiplexing system described in WO2004102542, a beam from inner pixels is used as a signal beam and a beam from outer strip shaped pixels is used as a reference beam in one spatial light modulator. Both beams are focused onto optical information recording media by using the same lens. The signal beam and the reference beam are caused to interfere with each other in the vicinity of a focal point plane of the lens, and holograms are recorded.
As for a marker retrieval technique at the time of hologram reproducing, there is, for example, JP-A-2008-139125 (Patent Literature 3). In JP-A-2008-139125, there is description “A hologram data area identification device 1 identifies a hologram data area, which is an area occupied by a hologram, from, a hologram image which is input from a photodetector. The hologram data area identification device 1 includes a frame buffer memory 3, an edge detection means 5, template comparison means 7, a template image storage means 9, and a centroid detection means 11.”